It is well known in the making of multi-layered products, such as resilient floor, wall or ceiling coverings, or desk, table or counter tops, and the like, that it is often necessary to bond together two or more layers of dissimilar synthetic polymeric materials and that it is often difficult to obtain strong and permanent bonds between such dissimilar synthetic polymeric materials.
Such difficulties often are believed to arise in the bonding of such dissimilar synthetic materials because of the difficulties created by the differences in their surface energies. For example, if atoms from two dissimilar synthetic polymeric materials cannot get close enough to each other, perhaps because of large dissimilarities or disparities in polarity, attractive van der Waals forces cannot be adequately taken advantage of to create strong permanent bonding. Nor is it believed that hydrogen bonding can be adequately taken advantage of in such situations. Many proposals have been made hitherto to overcome such difficulties and to improve the bond between such dissimilar synthetic polymeric materials but none has been found to be completely satisfactory in all respects to date.
The present invention will be described with particular reference to the bonding of dissimilar synthetic polymeric materials, such as, for example, vinyl resins and UV curable acrylated polyurethane resins but it is to be appreciated that the principles of the present invention are equally applicable to other equivalent dissimilar synthetic polymeric materials. In the same way, the present invention will be described with specific reference to multi-layered products, such as, for example, resilient floor coverings utilizing dissimilar synthetic polymeric materials but, again, it is to be appreciated that the principles of the present invention are equally applicable to other multi-layered products which also utilize dissimilar synthetic polymeric materials.
In the manufacture of resilient floor coverings, normally, a relatively flat base layer or substrate is laid out in substantially horizontal condition. Such a base layer or substrate is usually a felted or matted fibrous sheet of overlapping, intertwined filaments and/or fibers, usually of asbestos or of natural, synthetic or man-made cellulosic origin, such as cotton or rayon, although many other forms of sheets and films or textile materials, fabrics or the like, may be used.
Upon this substantially flat, horizontally positioned base layer or substrate is then deposited or applied a substantially uniform base layer of a liquid or semi-liquid resinous composition which contains a synthetic polymeric material, usually an ungelled polyvinyl chloride plastisol and normally containing a blowing or foaming agent.
This liquid or semi-liquid plastisol vinyl resin composition is subsequently firmed or gelled at an elevated temperature to a relatively more stable condition by procedures which are conventional and well known in the art. This relatively firm, gelled plastisol may then be printed with a decorative, multicolored pattern or design in which certain predetermined areas may contain a blowing or foaming inhibitor which subsequently modifies or alters the action of the blowing or foaming agent in those certain predetermined areas. Several different printing ink compositions may be used in such procedures.
A substantially uniform wear layer usually of a clear liquid or semi-liquid resinous composition and usually comprising another ungelled polyvinyl chloride plastisol composition but generally not containing any blowing or foaming agent is then applied as a wear resistant coating to the surface of the base layer of the printed, firmed and gelled polyvinyl chloride plastisol and is subsequently gelled and firmed thereon, either as a separate operation or in a joint operation with a subsequent fusing, blowing and foaming operation of the base layer of polyvinyl chloride plastisol composition. Thus far, all is conventional and there is relatively very little difficulty in creating a strong and permanent bond or adhesion between the base layer of polyvinyl chloride plastisol composition and the wear layer which is also a polyvinyl chloride plastisol composition.
It is then frequently desired to provide a top surface coating to the surface of the polyvinyl chloride plastisol wear layer and it is often desired that such top surface coating be a UV (ultra violet) curable acrylated polyurethane resin, primarily because of its superior physical and chemical characteristics and properties. However, in many instances, it is found that the adhesion or bond between the vinyl resin wear layer and the UV curable acrylated polyurethane resin top surface coating is not as strong or as permanent as desired or required, especially in the final product. It is believed that such lack of strength and of permanency or lack of suitable resistence to delamination is due in part to the fact that the wear layer and the top surface coating are dissimilar synthetic polymeric materials.